What are Moonquakes? Exactly What They Sound Like

Ever experienced an earthquake? The shaking — sometimes severe, sometimes mild — starts as quickly as it stops, the result of movement deep within the Earth’s layers. We feel the vibrations because of seismic waves, energy that “radiates outward from the fault in all directions,” according to the U.S. Geological Survey, “like ripples on a pond.”

Believe it not, something similar happens on the moon, and it’s called — you may have guessed it — a moonquake.

From the late 1960s until 1977, seismometers, instruments that track seismic activity, sat on different landing sites on the moon. Astronauts from four different Apollo missions brought back data from these machines, Trudy E. Bell writes for Science@NASA. What they revealed was astonishing.

Dozens of moonquakes took place during the time the instruments measured data, several registering 5.5 on the Richter scale. For reference, some of the biggest earthquakes measure 8.0 or higher on the scale, with the biggest ever recorded a 9.5 in Chile in 1960. A 5.0 can still displace heavy objects and crack plaster.

We also learned from the seismometers that four types of moonquakes exist: deep moonquakes likely caused by tides, meteorite-induced tremors, thermal quakes and shallow quakes. “The first three [are] generally mild and harmless,” Bell reports. But the shallow quakes, those events moved the Richter scale the most and “tended to last five times longer than on Earth,” she added, some continuing for 10 minutes. On Earth, the worst of the worst earthquakes rarely surpass two minutes, typically spanning 10 to 30 seconds, according to the University of Utah Seismograph Station.

This all means that if we’re ever to build on the moon, the infrastructure should probably follow the lead of places like San Francisco and the entire state of Alaska (it sees a magnitude 7.0 quake at least annually, notes the USGS). We also need more precise information about where the moonquakes formed. “The Apollo seismometers were all in one relatively small region on the front side of the moon,” said Clive R. Neal, associate professor of civil engineering and geological sciences at Notre Dame, to Bell. “We’re especially ignorant of the lunar poles.”

What’s more, Neal reveals, this could be happening on other planets, too. “The moon is a technology test bed for establishing such networks on Mars and beyond,” he said. Saturnquake, anyone?